Reinforcements and a reinforcement system for stabilized earth

ABSTRACT

New armatures and system using them, applicable to reinforced or armored masses of earth, which present a non planar section, with surrounding retainers having improved technical characteristics of traction resistance and friction surfaces.

The present invention relates to improvements to or in connection withreinforcements for use in stabilized or framed earth masses.

PRIOR ART

The technique of stabilizing earth masses by incorporation of flexiblereinforcements in the mass itself is in general use throughout theworld, and at the present time the basic theoretical principles of itsoperation are known fairly accurately, these principles having beenoriginally established in British Patent No 1069361 of Henri Vidal,which is now in the public domain, and being briefly summarized below inorder to provide a complete statement of the invention.

A mass of natural, unstabilized ground has a potential sliding orfracturing surface, which was initially established by Coulomb as aplane and which, usually passing through the foot of the outer surfaceof the mass, forms an angle dependent on the internal angle of frictionof the ground, with a value of approximately 63° in relation to thehorizontal for ground habitually used for this type of construction.Other forms of sliding surface, of circular and generally curvilineardevelopment, are closer to reality. In all cases ground situated on thissurface is called an "active wedge".

The fixing of this "active wedge" by means of a resistant front face iswhat concerns the construction of traditional walls. Fastening it byjoining to the ground at the rear, from a front face of lowerresistance, is what constitutes the anchored wall technique.

The inclusion of reinforcements distributed in the ground of the massmodifies the characteristics of the latter, so that the boundary of the"active wedge" is situated substantially nearer the outer boundarysurface of the mass, with an inclined plane development at the base,which becomes vertical from a certain height onwards, to a separationclose to 0.3 H from said outer surface, H being the mechanical height ofthe mass. Numerous trials and actual measurements made in the last 20years for the different reinforcement methods employed confirm that theboundary of the "active zone" practically coincides with the position ofthe maximum tensions in the reinforcement elements. This means that theinclusion of reinforcements distributed in the ground modifies andimproves the behaviour of the ground by giving it a certain anisotropy.

These principles have given rise to numerous methods of reinforcementconsisting of a more or less light, deformable face, from whichreinforcement elements extend towards the ground to be stabilized, insuch a manner as to pass across the boundary of the "active zone" andextend over a sufficient length--the "resistant zone"--for thefrictional forces of the reinforcement elements relative to the groundto exceed the maximum tension values developed in them (see FIG. 1). Itis found that these frictional forces do not develop in a useful mannerbeyond a distance of 0.8 H of the face, even with low values of H, withthe exception of special cases in respect of load and/or configurationof the slope on the mass.

The friction capacity of each reinforcement element is obviouslydependent on the useful length behind the "active zone", on the pressurewhich the ground exerts on its surface, on the area of contact and onthe nature of the surface material of the element, which is translatedinto the coefficient of friction between said material and the ground.

The reinforcements are generally incorporated in the earthwork insuccessive layers, over which extends a certain thickness of ground,which is compacted and over which is laid the following layer ofreinforcements, this pattern being repeated until the total height ofthe mass is reached. The whole arrangement must be sufficiently stableto support the thrust of the ground at the rear and the thrust of theloads acting on it, with the safety coefficients required.

With these methods, and in a general way, in order to ensure sufficientfrictional interaction of the reinforcement elements, it is convenientfor a minimum of some 2%, and preferably some 5%, of the area of thestratum of earth on which each layer of reinforcements is laid to becovered with the material of which the latter are made, and for at leastfour reinforcement levels to be provided.

The tensile strength of the reinforcements must thus on the one hand besufficient to withstand the horizontal forces caused by the thrust ofthe ground and the loads acting on the latter, a certain flexibility ofsaid reinforcements being convenient in order to permit adaptation tothe movements of the reinforced mass, while their properties areretained. This requirement is dependent on the tensile strength of thematerial of which the reinforcements are made and on the area of thelatter, and is a determinant factor in the neighbourhood of the line ofmaximum tensions.

On the other hand, the reinforcements must provide for the ground asufficient area of contact to mobilize frictional forces capable ofbalancing the maximum tension over a reasonable length. The requirementin the "resistant zone" is therefore the total area in contact andtherefore the perimeter of the section of the reinforcements and length,the area of said zone not being a determinant factor.

It is in the achievement of this compromise that the improvements andperfections of the reinforcement elements have been developed, becausethe reduction of the length of the reinforcements, without increasingtheir number, reduces the required volume of the fill selected andtherefore the cost of the construction work.

The frameworks or reinforcements were originally in the form of bands,in which the perimeter:area ratio reaches the highest values, this stepforward corresponding to British Patent No 1069361, in which use wasmade of thin metal bands of a length greater than 0.7 H, with uniformcharacteristics over their entire length.

A first improvement in the initial process is evidently the use of bandshaving a different width in the "resistant zone", which is difficult toapply in practice.

One way of reducing the resistant length while maintaining the areapresented would be to increase the value of the coefficient of frictionbetween the ground and the material of the bands, by means ofcorrugations, fluting or ribbing of slight height in the horizontalsurfaces of the bands, this process being within the scope of BritishPatent No 1563317.

In Patent Application PCT WO-95/11351 a distinction is made between thetwo functions of the bands, concentrating requirements in respect ofsection by means of concentrated cores of resistant material, to whichare integrally added either other, lighter, less expensive material inorder to obtain the required surface of the band with an improvedfinish, or plane lateral extensions of the same material.

In Patent No 2014562 a shortening of the length of the mass to less than0.65 H is achieved, while the same number of reinforcement bands isretained, by bifurcation of the bands in the last third of the latter,that is to say doubling the surface presented to the ground in part ofthe "resistant zone".

To sum up, all the processes consist of an increase of the resistance toextraction of the bands by means of improvements of the coefficient offriction or enlargement of the surface presented by the bands to theground fill, at least in the "resistant zone", in order thus tostabilize the frontal "active zone".

In any case, as the patents themselves show: "The area of reinforcementin contact with the earthwork is calculated so as to ensure that thereinforcements cannot be extracted by pulling".

The difference and the advantage of the present invention is clear. Withthe same increase of material, the application of the patent ES 452262,by means of the formation of ribs on the bands, does not achieve anyincrease of frictional surface but solely and exclusively an improvementof the coefficient of friction between the bands and the ground. PatentApplication WO-95/11351 also does not create any frictional surfaceadditional to that of the side wings, but on the contrary considerablyincreases the cost of material additional to the core.

DESCRIPTION OF THE INVENTION

In the present invention flexible reinforcements are presented forground stabilization, which, as is natural for this purpose, areequipped with a front end for anchoring by conventional methods to theelements constituting the outside skin or face, and whose functioning inrespect of resistance and friction is distinguished as follows:

A) Its resistant section (FIG. 2, 1) is not determined by perimeterrequirements, so that compact, non-plane shapes can be used with a lowperimeter:area ratio, including hollow configurations in which saidratio relates to the external perimeter.

B) Requirements in respect of friction are met by providing the compactresistant section with retaining modules (FIG. 2, 2), which surround itand which are so spaced that the surface in frictional contact with theground is formed by a cylinder or prism, having a straight generatrix,of the ground itself (FIG. 2, 3) and confined between the retainingelements, in such a manner that the perimeter is the exterior of theretaining elements (FIG. 3, D) and the coefficient of friction is thatcorresponding to ground-to-ground, that is to say the maximumattainable.

The materials of which these reinforcements can be made are preferablymetallic, preferably based on iron or steel. A variant contemplated inthe present invention is that the material of the reinforcement iscomposed, entirely (core plus retaining modules) or partially (core orretaining modules), on the basis of polymeric material. Anotherpreferred embodiment of the invention is for the core and/or retainingelements to be formed from cement material, for example concrete. Forthese purposes the material of which the core of the reinforcement ismade and that of the retaining modules need not be the same. That is tosay, the scope of protection of the present invention includescombinations: metallic core-retaining modules of polymeric material, orvice versa. The same type of combinations would apply in the case ofconcrete.

The results of the trials carried out in the laboratory indicate that,if the height of the retaining elements is greater than 3 mm andprovided that their spacing does not exceed 60 times their height, theextraction responds to the ground breaking point values on the surfaceof the assembly comprising the reinforcement-ground cylinder, theresidual value responding to the ground-ground coefficient of friction,thus achieving the qualification of the reinforcements as "highadhesion" in the general technique of Reinforced or Framed Grounds (FIG.4). According to these tests the reinforcements forming the subject ofthe present invention comply with all the requirements for high adhesionreinforcements, with pairs of values all above the line (2).

The advantage in comparison with the prior art is undoubted, because itbecomes possible to comply with requirements for reinforcements inrespect of friction, without any preconditions whatsoever with regard totheir tension-resistant section, through the addition of a small amountof material, which may be the same as or different from that of theresistant section, thus making it possible to take advantage of theshear resistance characteristics of the ground itself.

Thus, as particular examples of embodiment of the invention and moreconcretely for circular cylindrical configurations, we can cite by wayof illustration, and without any limitative character, the details shownin the following table.

                  TABLE I                                                         ______________________________________                                                D. Retaining .increment. Material:                                                                   .increment. Frictional                         D. Core elements     Cost      area                                           mm      mm           %         %                                              ______________________________________                                         8      14           7         75                                             12      22           10        83                                             16      26           8         62                                             ______________________________________                                    

in each case with an improved coefficient of friction.

Although there are no great differences in the tensional stress on thereinforcements in comparison with other reinforcements described in theprior art, since this depends solely on the nature of the material andthe resistant area, the gain in friction is clearly advantageous incomparison with high-adhesion reinforcement bands having the same area,as is shown in the illustrative examples, which do not have a limitativecharacter, shown in the following table.

                  TABLE II                                                        ______________________________________                                                    D. Retaining                                                                            .increment. Frictional surface:                         D. Core     elements  material ratio                                          mm          mm        %                                                       ______________________________________                                        8           14        115                                                     8           18        142                                                     16          26         43                                                     ______________________________________                                    

In view of the fact that the different standards which exist for thedimensioning of Reinforced or Framed Grounds require over-thicknessrepresenting a sacrifice to corrosion, the advantage of thereinforcements of the invention is impressive in providing compactsections having a low perimeter:area ratio, which will always entail ahigher useful area:total area ratio than with plane reinforcements orbands, and this in turn permits the use of greater thicknesses which areeconomically prohibitive for the latter.

As will be appreciated, with this type of reinforcements the latter canbe shorter than the usual uniform reinforcements which have the sameresistant section and of which the same number are used, and it will bepossible to use a smaller number of them or to use a smaller section forone and the same length. In addition, because of the advantagesindicated above there is nothing to prevent the manufacture ofreinforcements having a low unit weight, so that requirements in respectof resistance can be met gradually and accurately. In any case, theresult will be a considerable saving, either in the volume of fillrequired or in the actual cost of the reinforcement material.

Comparative calculations made for one and the same mass, with anoverload of 1 t/m² and an internal angle of friction of 30°, equippedwith plain bands, ribbed bands and reinforcements according to theinvention, produce the following results:

                  TABLE III                                                       ______________________________________                                                                           Reinforcement                                       H.L.       Plain    Ribbed                                                                              according to                               Mechanical                                                                             Reinforcement                                                                            band     band  the invention                              m        m          kg/m.sup.2                                                                             kg/m.sup.2                                                                          kg/m.sup.2                                 ______________________________________                                         6       4.5        18       13.25  9                                         12       9          32       25    19                                         ______________________________________                                    

The invention is applicable to masses of all heights, since it ispossible to adapt the section to requirements in respect of resistanceand to adapt the dimensions of the retaining elements to requirements inrespect of friction.

None of the general indications of present processes, in respect of theneed for a certain ratio between the area of the ground bed on whicheach layer of reinforcements to be covered is laid and the material ofthe reinforcements, applies to the process of the invention.

EXPLANATION OF THE DRAWINGS

FIG. 1: Resistance diagram in which 1 represents the core of thereinforcement, 2 the retaining module and 3 the mobilized ground. D andd are respectively the width (diameter in the case of circularstructures) of the mobilized volume of earth and of the core+themobilized volume of the reinforcement. A represents the so-called"resistant zone" and B the so-called "active zone", while L is thedistance between retaining modules (2).

FIG. 2: Three-dimensional representation of a reinforcement composed ofthe core (1) having a non-plane section and the retaining module orretaining element (2). In the representation it is possible to see themobilized volume of earth (3) between retaining modules.

FIG. 3: Section of a retaining module in which d is the diameter of thecore and D the diameter of the core+the mobilized volume.

FIG. 4: Representation of the coefficient of friction (Y) plottedagainst vertical pressure in KN/m² (X). The line 1 corresponds to plaintie rods and the line 2 to high-adhesion tie rods. At point 3 are shownthose pairs of values which are outside the scale represented (>3).

FIG. 5: Reinforcement of solid, square section with retaining elementssurrounding the core and having a square contour coinciding with thesection, with bevelled edges.

FIG. 6: Reinforcement of solid, triangular section with retainingelements surrounding the core and having a triangular contour coincidingwith the section.

FIG. 7: Reinforcement of solid, irregularly curved section withretaining elements surrounding the core and having an irregularly curvedcontour coinciding with the section.

FIG. 8: Reinforcement of solid, hexagonal section with retainingelements surrounding the core and having a hexagonal contour coincidingwith the section.

FIG. 9: Reinforcement of hollow, rectangular section with retainingelements surrounding the core and having a rectangular contourcoinciding with the section.

FIG. 10: Reinforcement of solid, square section with offset retainingelements half surrounding the core and having a U-shaped contour forminghalf-grooves.

FIG. 11: Reinforcement of solid, square section with tooth-shapedretaining elements.

FIG. 12: Reinforcement of solid, square section with retaining elementssurrounding the core and in the form of a helicoidal groove.

FIG. 13: Reinforcement of solid, square section with retaining elementssurrounding the core and in the form of spaced spike-like grooves.

FIG. 14: Reinforcement of solid, circular section with retainingelements in the form of half-rings.

FIG. 15: Reinforcement of solid, circular section with retainingelements in the form of teeth.

FIG. 16: Reinforcement of solid, circular section with retainingelements surrounding the core and forming a helicoidal ring.

FIG. 17: Reinforcement of solid, circular section with retainingelements surrounding the core and having circular spike-like contours.

The drawings show illustrative but not limitative embodiments of thepresent invention. Both the section of the core of the reinforcement andthe contour of the retaining elements may be regular (parallelepiped,triangle, circle, ellipse, hexagon, etc.) or irregular. The retainingelements may or may not be arranged to surround the core of thereinforcement, or be spaced, helical, offset subdivided into 2complementary parts, inclined relative to the perpendicular to the axisof the core, thickened, spike-like, etc. They may also have contoursprovided with bevelled or rounded edges, and these contours may or maynot coincide with the section of the core of the reinforcement, that isto say the perimeter of the retaining elements need not be parallel orhomothetic to the core (for example: circular core and rectangular orirregular retaining elements, or vice versa).

Their system of fastening to the reinforcement core may consist of anyof those described in the known art: adhesive bonding, filler metal orpressure welding, additional casting, production by co-extrusion,simultaneous casting, etc.

What is claimed is:
 1. A reinforcement for forming a reinforced orframed mass of earth comprising an elongate core element and a pluralityof retaining modules, each of said retaining modules being in contactwith and surrounding a discrete portion of the core element with each ofthe retaining modules spaced from one another, said retaining moduleshaving congruent shapes and protruding from the core element the sameheight such that, upon insertion of the reinforcement into the mass ofearth, at least first and second of the retaining modules confine earththerebetween to form a cylinder or prism with first and second basescomprising said first and second retaining modules respectively and withsides comprising the confined earth, wherein a distance the retainingmodules are spaced from one another and the height the retaining modulesprotrude from the core element are selected such that, upon insertion ofthe reinforcement into the mass of earth, the reinforcement achieves acoefficient of friction that, when plotted against vertical pressureacting on the reinforcement, is above line 2 of the graph of FIG.
 4. 2.A reinforcement for forming a reinforced or framed mass according toclaim 1, wherein the retaining modules protrude from the core element aheight of at least 3 mm and wherein the space between the retainingmodules does not exceed 60 times said height.
 3. A reinforcement forforming a reinforced or framed mass according to claim 2, wherein theheight that the retaining modules protrude from the core element isbetween 6-10 mm.
 4. A reinforcement for forming a reinforced or framedmass according to claim 1, wherein the core element is hollow.
 5. Areinforcement for forming a reinforced or framed mass according to claim1, wherein the core element is solid.
 6. A reinforcement for forming areinforced or framed mass according to claim 1, wherein the core elementand the retaining modules comprise the same material.
 7. A reinforcementfor forming a reinforced or framed mass according to claim 1, whereinthe core element comprises a different material than the retainingmodules.
 8. A reinforcement for forming a reinforced or framed massaccording to claim 1, wherein the core element, the retaining modules orboth are metallic.
 9. A reinforcement for forming a reinforced or framedmass according to claim 1, wherein the core element, the retainingmodules or both are of a polymeric material.
 10. A reinforcement forforming a reinforced or framed mass according to claim 1, wherein thecore element, the retaining modules or both are cementitious.
 11. Areinforcement for forming a reinforced or framed mass according to claim1, wherein the core element, the retaining modules or both are concrete.12. A reinforcement for forming a reinforced or framed mass according toclaim 1, wherein the core element is metallic and the retaining modulesare a polymeric material or vice versa.
 13. A reinforcement for forminga reinforced or framed mass according to claim 1, wherein the coreelement is metallic and the retaining modules are cementitious or viceversa.
 14. A reinforcement for forming a reinforced or framed massaccording to claim 1, further comprising a face from which the coreelement extends.
 15. A reinforcement for forming a reinforced or framedmass according to claim 1, wherein the retaining modules are circular.16. A reinforcement for forming a reinforced or framed mass according toclaim 1, wherein the retaining modules are polyhedral.
 17. Aconstruction system comprising a plurality of reinforcements, includingthe reinforcement of claim
 1. 18. A construction system comprising aplurality of reinforcements, including the reinforcement of claim 14.19. A combination of the reinforcement of claim 1 and a mass of earth,said reinforcement being inserted in the mass earth and reinforcing orframing it.